Many transformations of organic compounds are catalytic processes mediated by metals. In such catalytic transformations, which include alkylation, ammination, oxidation, hydroformylation, and reduction, as a general proposition the metal is not utilized per se but is instead supported on an inert carrier to gain the benefits of increased dispersion. A characteristic of many common supported catalysts used with organic acid feedstocks is that the supported metal and the underlying carrier tend to leach into the liquid phase under reaction conditions. Using nickel on gamma-alumina as an example of a supported catalyst, in the presence of a highly corrosive feedstock of an organic acid both nickel and alumina tend to dissolve.
A disadvantage of such prior art catalysts is that the product contains relatively high levels of metal as a contaminant. Such a product may have considerably reduced commercial value because of the metal contamination, or may require relatively costly processing to remove such contamination before affording a commercially acceptable material.
Another disadvantage of such supports is their limited use in continuous processes. For example, where a fixed bed continuous process is desired it is clearly mandatory that the bed retain its physical integrity. But it follows just as clearly that such integrity is impossible where the carrier dissolves in the feedstock. Thus, many catalyst transformations of organic acids are presently unfeasible in a continuous mode because commonly used supports are structurally inadequate.
Still another disadvantage of prior art supports is that their tendency to leach makes subsequent catalyst regeneration difficult if not impossible. For example, leaching may cause a sufficient change in composition as to make regeneration impractical. It will be recognized that regeneration of a catalyst is highly desirable.
The limitations of prior art catalysts spurred our search for carriers, or supports, which would be sufficiently inert in the corrosive atmosphere of organic fatty acids as feedstocks, or as substantial components of feedstocks, to overcome the aforementioned disadvantages. In particular, we sought carriers whose levels of leaching are sufficiently low as to permit their use in a continuous, fixed bed process. We have discovered several carriers whose corrosion resistance in the presence of fatty acids makes possible a continuous, fixed bed process utilizing as a catalyst a metal(s) supported on these carriers.